1. Field of the Invention
The present invention relates to a wavelength-tunable light emitting device and, more particularly, to a wavelength-tunable light emitting device capable of being easily and flexibly tuned for emitting light of a desired wavelength.
2. Description of the Related Art
Conventional light emitting devices include semiconductor lasers, light-emitting diodes and solid-state lasers. Generally, light emitting devices are fixed-wavelength light emitting devices that emit light of a wavelength specific to a substrate employed therein to produce light. There is a previously proposed wavelength-tunable light emitting device, such as a solid-state laser capable of emitting light of variable wavelength variable in a predetermined wavelength range by utilizing crystal structure (e.g., phonon final level).
The prior art wavelength-tunable light emitting device needs to employ a material of a complicated crystal structure as its substrate and has difficulty in securing a sufficiently wide wavelength range in the visible region.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a wavelength-tunable light emitting device capable of being easily and flexibly tuned for emitting light of a desired wavelength.
The present invention provides a wavelength-tunable light emitting device including: a first member; a second member spaced from the first member through a vacuum space or a transparent insulating member; and a variable-voltage power supply for applying a voltage between the first member and the second member to cause a tunnel current to flow, said variable-voltage power supply being adapted to vary the voltage applied between the first member and the second member. In the present invention, the gap between the first member and the second member is set at a few nm in length so that light emission from a local region, i.e., a tunneling region, in which the tunnel current flows, is induced by the optical transition between the respective localized states of the first member and the second member.
It is preferred that the first member and the second member are made of a material that restrains light emission caused by recombination of electrons and holes. Also, it is preferred that the device of the present invention further comprises means for inducing surface plasmons of the first member or the second member to intensify the light emitted from the tunneling region.
Also, it is preferred that the first member and the second member are formed by defining patterns in a layer that is formed on an insulating support. In addition, it is preferred that the first member and the second member are layers that are layered on an insulating support, with the first member and the second member being layered via a transparent insulating layer so as to form the gap between the first member and the second member.
According to the present invention, the variable-voltage power supply applies a voltage between the first and second members, which are closely spaced from each other by a few nm in length so as to cause a tunnel current to flow through the vacuum space or the transparent insulating member. Therefore, the light emission from the tunneling region is induced by the optical transition between the respective localized states of the first and second members; and thus, the wavelength of the light emitted from the tunneling region can be easily and flexibly varied by varying the voltage applied between the first member and the second member. In addition, since the light can be emitted from a very small local region in which the tunnel current flows, the wavelength-tunable light emitting device of the present invention can provide a minute wavelength-tunable light source of a size of an atomic scale.